Year	Years
1970	0.37
1971	0.38
1972	0.39
1973	0.41
1974	0.42
1975	0.44
1976	0.45
1977	0.47
1978	0.49
1979	0.5
1980	0.52
1981	0.54
1982	0.56
1983	0.58
1984	0.6
1985	0.63
1986	0.65
1987	0.67
1988	0.7
1989	0.72
1990	0.75
1991	0.78
1992	0.81
1993	0.84
1994	0.88
1995	0.91
1996	0.95
1997	0.99
1998	1.03
1999	1.07
2000	1.11
2001	1.15
2002	1.2
2003	1.24
2004	1.29
2005	1.33
2006	1.38
2007	1.43
2008	1.48
2009	1.53
2010	1.58
2011	1.64
2012	1.69
2013	1.75
2014	1.81
2015	1.86